The present invention relates to a multipolar wiggler for imparting periodic magnetic fields to electron beams to obtain laser beams or radiated beams with a cyclotron or a linear accelerator.
A multipolar wiggler is used to produce radiated beams by deflecting in a undulating pattern the orbit of charged particles, such as electrons, accumulated in a cyclotron or a linear accelerator. One example is disclosed in literature titled Nuclear Instruments and Methods in Physics Research 172 (1980) at pages 45-53. As shown in FIG. 5, this wiggler comprises a pair of rows of permanent magnets 1-4 and 1'-4'. The magnets are arranged so that the magnetized directions (shown by arrows) are arranged periodically. The corresponding upper and lower magnets are arranged so that different poles face each other. Thus, periodic magnetic fields are produced around the electron beam.
As is apparent from FIG. 5, the magnets 1-4 and 1'-4' of a conventional multipolar wiggler each have a rectangular shape elongate in a direction X and are arranged periodically as described above, with the electron beam orbit 5 extending in a direction Z between the upper and lower rows. The magnetic field produced around the electron beam orbit 5 is thus constant near the center of the electron beam orbit 5 with respect to the direction X (FIG. 6). Thus, there is some possibility that the electron beam may be deflected out of the multipolar wiggler depending on the state of the electron beam when entering the multipolar wiggler.
This problem is discussed in detail in Nuclear Instruments and Methods in Physics Research A304 (1991) on pages 753-758. This literature further states that this problem may be solved by applying a focusing force in the direction X to the electrons in the multipolar wiggler, and as a specific means for solving this problem, proposes multipolar wigglers as shown in FIGS. 7a to 7d. The wiggler shown in FIG. 7a has the upper and lower magnets curved over the entire width thereof. The magnets of the wiggler in FIG. 7b are curved only at their central parts with respect to the widthwise direction. The wiggler of FIG. 7c comprises trapezoidal magnets and the wiggler of FIG. 7d uses trapezoidal and diamond-shaped magnets in combination.
The multipolar wigglers shown in FIGS. 7(a)-7(d) are all structurally complicated compared with the wiggler shown in FIG. 5 and the manufacture of the magnets is difficult. Moreover, in any of the wigglers, the focusing force imparted to the electron beam is constant, so that it is difficult to adjust the focusing force after the wiggler has been completed even if the focusing force is too strong.